Did the world's sexiest zoo get too sexy?

The Cincinnati Zoo and Botanical Garden, once called "the world's sexiest zoo," is dishing out birth control to its animal inhabitants.

Janet Hutson, the Jungle Trails senior keeper at the Cincinnati Zoo & Botanical Garden, gives a Bonobo a mixture of yogurt and a crushed birth control pill at the zoo.(Photo: Glenn Hartong, The Cincinnati Enquirer)

Story Highlights

Methods used include vaccines, hormonal implants and human birth control pills

Permanent birth control methods are not generally used on endangered species

Breeding has been on hold to guard against the bloodlines of Cincinnati's gorillas

CINCINNATI -- Newsweek magazine once called it "the world's sexiest zoo."

So it might come as a surprise that the Cincinnati Zoo and Botanical Garden takes contraception as seriously as it does breeding, as do other U.S. zoos. Animal births may make headlines, but behind the scenes, great effort goes into preventing unwanted pregnancies. The zoo earned that nickname because of its phenomenal success with its breeding program. And it burnished that reputation last month with the much ballyhooed birth of a female giraffe.

"It is a very important part of what we do. It's being responsible," says Terri Roth, the zoo's vice president of conservation and science.

Contraception is one piece of the giant jigsaw puzzle of managing captive animals. Before animals breed, zoos must consider factors such as space constraints -- both now and in the future -- social groupings and the need to sustain healthy, genetically diverse populations.

An hour and a half before the first visitors enter the zoo, Ron Evans is well into his morning routine inside Gorilla World. The zoo's primate team leader sets out small cups, each marked with a gorilla's name. Some gorillas will get fiber; some take Vitamin E because of dry skin.

All six females will get a birth control pill, the same as a human would take.

Evans crushes each pill between two spoons, then sprinkles the powder over yogurt, a treat the gorillas love. He dares not give them uncrushed pills.

"These guys are so smart," he says. "You think they've swallowed it, and they tuck it under their tongue and spit it out when you're not looking."

Evans then visits Samantha, a mother of six, and spoon-feeds her the yogurt. "Good girl," he says.

He works his way down the line of stalls: M'linzi and Chewie, then Anju, Asha and Mara.

Forty-eight gorillas have been born here, but none since 2006. "We're a little bit of a victim of our own success," Evans says.

Cooperation key

Breeding has been on hold to guard against the bloodlines of Cincinnati's gorillas being overrepresented in the North American population. Studies have shown that highly inbred animals are more susceptible to disease, have higher rates of infant mortality and are more likely to have developmental abnormalities.

Years ago, when zoo populations were unmanaged, a flurry of births might be followed by long periods of breeding inactivity. Populations aged and eventually crashed. Then zoos captured more animals from the wild.

But by the 1970s, with the list of endangered species growing rapidly, it became ethically and sometimes legally impossible for zoos to replenish animals that way.

So in 1981, the Species Survival Plan (SSP) was established to manage the breeding of certain species. It is administered by the Silver Spring, Md.-based Association of Zoos and Aquariums, whose membership of 223 accredited institutions includes the Cincinnati Zoo.

Today, "No zoo is an island," says Evans, who sits on the Gorilla SSP management committee. "We all have to cooperate to properly manage species."

That sometimes means moving animals from zoo to zoo to diversify the gene pool. Officials consult a "studbook" -- a breakdown of a population's vital records, including lineage -- before deciding which animals to breed and where.

Often, though, because of genetic considerations or limited space for animals, the recommendation is to not breed.

Many variables come into play

It's possible to simply separate males and females. But zoos are reluctant to split up compatible pairs because for many species, including gorillas, "it's better for the animals to be in a social group," Roth says. "And that's better for (zoos), because we don't have to have separate enclosures" that take up valuable space.

Spaying and castrating have long been used to keep zoo animals from reproducing. But because those methods are permanent, today they're generally not used for endangered species.

The job of assessing the effectiveness of contraceptives falls to the AZA Wildlife Contraception Center at the St. Louis Zoo. "Every time we're treating a new species, we are trying to figure out what's the right dose, how long it is going to be effective and what the reversal rate will be," says Cheryl Asa, the center's director.

The center recommends appropriate contraceptives to zoos. A vaccine, for instance, might be effective among hoofed animals. In Cincinnati, a langur, lar gibbon and siamang (all of which are primates) have received hormonal implants. A bonobo and orangutan take human birth control pills, as do the six female gorillas.

But changes are in store for two of those gorillas. Anju, who is 11, and Asha, 10, arrived here in the past year from zoos in Pittsburgh and Brownsville, Texas, respectively. The Gorilla SSP has determined it makes sense to breed them with Jomo, the zoo's 450-pound silverback.

Before they get pregnant, though, they must become acclimated to Jomo's family group, Evans says. And when that happens, perhaps this winter, the girls will go off the pill.